The present invention relates to an electronic apparatus for controlling ignition timing of an internal combustion engine, and, more particularly, to a knock controller for counting the number of knock pulse signals when knocking has developed, and which controls the ignition timing for each of the cylinders depending on the counted value of the knock pulse signal.
In recent years, attempts have been made to burn a lean fuel mixture in order to reduce the consumption of fuel in the internal combustion engine. However, if the lean fuel mixture is burned in a conventional engine, the output of the engine decreases. Therefore, attempts have been made to increase the compression efficiency of the engine to increase the output per unit A/F, in order to increase the engine output. Knocking, however, develops easily with an increase in the compression ratio of the engine. Knocking, which develops in the engine, is accompanied by a knocking sound, a reduction in the running performance and a generation of a counter torque which reduces the engine output and causes the engine to overheat so that it could break down. Knocking has a close relationship to ignition timing, and it is known that the engine produces its maximum output when the ignition timing, i.e., the ignition angle, is set to the point just before that at which knocking develops. Reduction in the advance of the ignition angle to avoid the development of knocking results in a decrease in the engine output. It is therefore desired to advance the ignition timing to the point just before that at which knocking develops. In an engine which is equipped with a turbo-charger and, in particular, a logic having a high compression ratio, it is necessary to obtain the optimum ignition timings in order to maintain the maximum efficiency. Therefore, it is conventional practice to bring the ignition timing back to the point just before that at which knocking develops, if knocking has developed.
In, for example, a conventional knock controller in a four-cylinder engine with a single knock sensor being installed, the development of knocking is detected by detection signals produced by the knock sensor, and the ignition timing for all of the cylinders are controlled under the same conditions by the knock signals of the single knock sensor. However, knocking is not properly detected and controlled due to different degrees of knocking produced in each of the cylinders or due to differences in detecting knocking that result from the place at which the knock sensor is installed in the engine.